docs: [#10] add twelve-factor app refactoring plan and guides

- Add comprehensive twelve-factor refactoring plan (README.md)
- Add detailed phase 1 implementation checklist
- Add step-by-step migration guide with backward compatibility
- Include Torrust Tracker-specific configuration considerations
- Address deployment separation and environment parity violations
- Plan multi-cloud support starting with Hetzner infrastructure
- Update project-words.txt with new technical terms
- All documentation passes markdown linting with table formatting fixes

Author: josecelano